Apparatus for stripping sulfur trioxide from oleum



Feb 4, 1947 J. J. BRADLEY ET AL Y2,415,159v

APPARATUS FOR STRIPPING SULFUR TRIOXIDE FROM OLEUM Filed- June 13. 1942 vLfoufz Llrad'lg INVENTORS Albert y,Rewns'clzt.

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/ ATTORNEY Patented F eb. 4, 1947 UNITED STATES PATENT OFFICE] APPARATUS FOR STRIPPIN G SULFUR TRIOXIDE FROM OLEUM corporation of Delaware Application June 13, 1942, Serial No. 446,858

(Cl. 23e-277) 3 Claims. l.

This invention relates to the production of pure sulfur trioxide and is particularly directed to methods and apparatus for stripping sulfur trioxide from oleum.

The manufacture of sulfur trioxide for the production of high strength oleum and for other industrial requirements for sulfur trioxide is commonly effected by stripping oleum in a suitable oleum still. Oleum of such strength as may conveniently be obtained with the dilute sulfur trioxide gases produced in a contact sulfuric acid plant is heated in a suitable still to drive olf the dissolved S03. It is common practice to pass the oleum in heat exchange with hot gases from the contact plant or simply to use combustion gases from any suitable source. The apparatus heretofore available has either been highly complicated, requiring much attention and supervision, or highly rudimentary subject to repeated failure of riveted or welded joints.

The present invention has for its object to avoid disadvantages of the prior art and to provide simple and effective methods and apparatus for stripping sulfur trioxide from oleum. An object is to provide simple and effective heat transfer. Another object is to provide apparatus of great` durability and freedom from failure of joints and seams. Still other objects Will be pointed out hereinafter.

These objects are accomplished by the embodiment of the invention illustrated in the drawing in which Figure 1 is a side elevation partially in section, Figure 2 is an end elevation taken along line 2 2, and Figure 3 is a sectional View taken along line 3--3.

According to the invention as illustrated in the drawing there are provided a plurality of elongated, cylindrical retorts I disposed horizontally on their axis. These retorts are constructed of seamless or welded and normalized steel tubes which are relatively long as compared with their diameters and each tube is arranged so that its axis is in a horizontal position. The ends are closed by suitable Welded-on caps 2 and 3 thereby forming a completely closed retort.

Adjacent one end of the tubes or retorts there` isprovided inlet means 4 through which the oleum to be distilled or stripped is introduced into the retorts. Adjacent the other end there is provided outlet means 5 through which the spent acid, that is, the oleum stripped of the bulk of its dissolved S03, is continuously withdrawn from the retort. 'Ihe outlet 5 is located in the cap 3 in order to actas overovv. means `whereby a predetermined level of oleum may be maintained in the retort. The tube is also provided with-a' flushing outlet 6 for cleaning out the retort. Gas* outlet means 1 and 8 are also provided in the top of the retort. These are located centrally of the lengthof the tube and communicate With the multiple manifolding arrangement.` shown at 9 and lil. The thermometer Well I`I= is provided adjacent the outlet end so that temperature ofthe acid being discharged can be observed.

Each tube l' is provided interiorly`- and intermediate betweenthe inlet 4 and the' outlet 5 with one or more baffles, such as illustrated at l2, tol impede the flow of liquid in the tube. Each of these bailies extends to the liquid level, as de'- termined by the outlet 5, and is provided with an opening I3 at the bottomto provide for drain`` age of each compartment when the flushing outlet 6 is being used.

The lower half of the tubes are exposed toV a heat transfer fluid Which suitably may 'be the hot gases from the burnerrld. These hot gasesI are directed up into contact With the bottom por-v tions of the tubes l by a brickwork furnace construction !5 of any suitable design and contact the tubes throughout the length of the elongated heating chamber I6 through which the hot gases pass in a direction countercurrent to the flow of the liquid through the tubes before passing out through the stack connectionV l1.

In order to provide means for confining the heat transfer fluid and for isolating the upper portion of the tubes, that is to say, the portion of the' tube above the liquid level, from the heat trans-- fer fluid the arch I8 of the furnace structure is i brought over to abut the sides of the tubes I so' as to leave about one-half of the tubes Within the heating chamber I6 exposed to the heat transfer medium and the other half isolated there-` from. The ends I9 of the furnace structure are terminated short of the ends of the tubes l in order that the Welded caps 2 and 3 also may be isolated from the hot heat transfer fluid. In other words, the tubesare in effect embedded in the arch of the furnace so thatthe bottom portion of the tubes is exposed to the hot furnace' gas and the top part of the tube is exposed to the atmosphere. This provides for eiectivef heat transfer to the liquid and at the same time prevents local overheating. f

Means for supporting the tubes in the furnace structure comprise the stirrups 20 which arev Welded to the upper portion of the tube which is exposed to the atmosphere. These stirrups are slung bythe rods 22 from the I-beamsf2l which form part rofl the: usual.A .reenforcement'.l for-1' th'el furnace structure. The tubes are thus suspended in the furnace and their position may be adjusted initially by the nuts 23 and 24 on the rod 22.

Thus there is provided an arrangement in which the welded joints are all subjected to the cooling influence of the atmosphere or the contents of the still. Thus the welded caps 2 and 3, the inletA 4, the outlet 5, the flushing outlet 6 and the gas outlets 1 and 8, the thermometer well Il, and the stirrups 20 are all s o located that their welded joints are exposed to the cooling influences of the atmosphere, and the welded internal baffles l2 act as ns conducting the heat away from the welds into the acid contained in the tube. One of the essential points in the entire structure is that no projections of any kind are exposed to the iiames. Such projections would conduct additional heat to the retort shell and cause local overheating, with resulting corrosion and eventual failure. Thus the apparatus is preserved against the deteriorating effects of the oleum, acid spray or S03 on welded joints and locally overheated portions.

l It will be observed here also that the welded joints between the stirrups 20 and the tubes l are also exposed to the atmosphere and isolated from the hot furnace gases, though it is not so important in this instance since the welded joint here is not exposed to the hot oleum. Should the tubes I be of welded and normalized structure the Welded joint also is preferably located in the part of the tube exposed to the atmosphere and isolated from the hot furnace gases.

In operation of the still oleum of suitable.'

strength is continuously fed to the tube through the inlet 4 and the stripped oleum is continuously withdrawn from the tubes through the outlet 5. The outlet 5 acts as an overiiow means to maintain the oleum in the tube at the proper level whereby all the portions of the tube exposed to the hot furnace gases are 'covered by the liquid. The baille plates I2 act to impede the iiow of oleum in the tube and help to keep oleum of the high strength fed to tube segregated from the low strength stripped oleum withdrawn through the outlet 5. The feed is regulated by observing the temperature of the oleum adjacent the outlet end by means of the thermometer well Il. Thus if the rate of feed is regulated so that the temperature at the outlet end is about 225o C. then all but about 2-5% of the available S03 will have been stripped fromv the oleum. It is not necessary, however, to effect Vsuch complete stripping and in some installations it may be found desirable only to strip a few percent of the available oleum in view of the lower temperatures which can thus be` maintained. The high strength oleum very readily gives up its S03 whereas more and more heat is required as the oleum becomes nearer the monohydrate. Thus by the arrangement in which the iiow of the heat transfer fluid is countercurrent to the flow of the acid in the tube greatest heat economy is effected.

While we have disclosed our invention with reference to particular apparatus it will be understood that variations may be made therein without departing from the spirit of the invention. Within the scope of the appended claims such Variations are understood to be part of the invention.

We claim:

1; Apparatus for heating liquids comprising a furnace structure having an elongatedl heatingV chamber defined in part by sidewalls and endwalls, at least one metal tube the axis of which is rectilinear disposed between said side walls extending the length of said heating chamber and having its ends extending beyond said end-walls, supporting means resting on said sidewalls and hangers depending therefrom and welded to the top of said tube for supporting said tube between said sidewalls, and an arch extending transversely across said heating chamber so located with respect to said tube that a portion of the tube is above said arch and a portion is below said arch, said tube being seamless in the portions extending into the heating chamber and having welded joints in the portions outside of said heating chamber.

2. Apparatus for heating liquids comprising an elongated tube, the axis of which is rectilinear, mounted in a position horizontal to its axis, inlet means adjacent one end of said tube for admitting liquid, outlet means adjacent the other end for withdrawing liquid, overflow means for maintaining a predetermined level of liquid in said tube, baille means extending from one side of the tube to the other side for impeding the iiow of liquid from the inlet end to the outlet end, said inlet and outlet means being so correlated with said baffle means that the direction of ow of liquid in the tube is from the inlet end to the outlet end exclusively, and means for conducting heating medium along the bottom of said tube countercurrent to the ow of liquid therein along and in contact with the bottom of said tube.

3. Apparatus for heating liquids comprising a furnaceV structure having an elongated heating chamber defined in part by side walls and end walls, at least one metal tube the axis of which is rectilinear disposed between said side walls and extending the length of said heating chamber, said tube having its ends extending beyond said end walls, an arch extending transversely across said heating chamber so located with respect to said tube that a portion of the tube-is above said arch and a portion is below said arch, and means for supporting said tube in the above stated relation to said side walls, end walls and arch, said tube being seamless in the portions extending into the heating chamber and having welded joints in the portions outside said heating chamber.

JOHN J. BRADLEY. ALBERT REGENBRECHT.

REFERENCES CITED The following references are of record in the le of this patent:

UNITED Vstclrrizs VPrrrErrrs British Nov. 18, 1938 

